Gαs-Biased β2-Adrenergic Receptor Signaling from Restoring Synchronous Contraction in the Failing Heart

Cardiac resynchronization therapy (CRT), in which both ventricles are paced to recoordinate contraction in hearts that are dyssynchronous from conduction delay, is the only heart failure (HF) therapy to date to clinically improve acute and chronic function while also lowering mortality. CRT acutely enhances chamber mechanical efficiency but chronically alters myocyte signaling, including improving beta-adrenergic receptor reserve. We speculated that the latter would identify unique CRT effects that might themselves be effective for HF more generally. HF was induced in dogs by 6 weeks of atrial rapid pacing with (HFdys, left bundle ablated) or without (HFsyn) dyssynchrony. We used dyssynchronous followed by resynchronized tachypacing (each 3 weeks) for CRT. Both HFdys and HFsyn myocytes had similarly depressed rest and beta-adrenergic receptor sarcomere and calcium responses, particularly the beta(2)-adrenergic response, whereas cells subjected to CRT behaved similarly to those from healthy controls. CRT myocytes exhibited suppressed G alpha(i) signaling linked to increased regulator of G protein (heterotrimeric guanine nucleotide-binding protein) signaling (RGS2, RGS3), yielding G alpha(s)-biased beta(2)-adrenergic responses. This included increased adenosine cyclic AMP responsiveness and activation of sarcoplasmic reticulum-localized protein kinase A. Human CRT responders also showed up-regulated myocardial RGS2 and RGS3. Inhibition of G alpha(i) (with pertussis toxin, RGS3, or RGS2 transfection), stimulation with a G alpha(s)-biased beta(2) agonist (fenoterol), or transient (2-week) exposure to dyssynchrony restored beta-adrenergic receptor responses in HFsyn to the values obtained after CRT. These results identify a key pathway that is triggered by restoring contractile synchrony and that may represent a new therapeutic approach for a broad population of HF patients.